Leadville, Colo. (AP) Water in a mine drainage tunnel north of Leadville is building up pressure and could blowout, leaving officials worrying that it could cause catastrophic damage to the historic mining town and contaminating the Arkansas river.

State, federal and county officials will have a conference call At 11 a.m. Thursday to determine how to deal with the millions of gallons of water in the Leadville mine drainage tunnel. Ground seepage from increased snow levels is adding further pressure on the blockage, said Polly White of the Colorado division of Emergency management.

The tunnel is believed to have become blocked years ago by a partial collapse.